U.S. patent number 5,356,949 [Application Number 07/837,117] was granted by the patent office on 1994-10-18 for adhesive composition comprising (meth)acrylate polymer and epoxy resin.
This patent grant is currently assigned to Lintec Corporation. Invention is credited to Kazuyoshi Ebe, Mikio Komiyama, Yasunao Miyazawa, Takanori Saito.
United States Patent |
5,356,949 |
Komiyama , et al. |
October 18, 1994 |
**Please see images for:
( Certificate of Correction ) ** |
Adhesive composition comprising (meth)acrylate polymer and epoxy
resin
Abstract
An adhesive tape comprising an energy beam transmittable base
sheet having a surface tension of not more than 40 dyne/cm and an
adhesive layer formed on one surface of the base sheet, the
adhesive layer comprising a (meth)acrylate polymer, an epoxy resin,
a photopolymerizable low molecular weight compound, a heat
activatable latent curing agent for the epoxy resin and a
photopolymerization initiator for the photopolymerizable low
molecular weight compound. The adhesive in the adhesive layer is
curable with an energy beam and the so cured adhesive develops
tackiness again when heated. When the tape is used in processing a
semiconductor wafer, it serves as a dicing tape for holding the
wafer in position during the dicing step. Each piece of the diced
and cured adhesive layer, that is attached to each chip and capable
of being tackified by heating, provides an adhesive required for
securely mounting the chip on the lead frame in the die-bonding
step.
Inventors: |
Komiyama; Mikio (Yokohama,
JP), Miyazawa; Yasunao (Urawa, JP), Ebe;
Kazuyoshi (Minamisaitama, JP), Saito; Takanori
(Ohmiya, JP) |
Assignee: |
Lintec Corporation (Tokyo,
JP)
|
Family
ID: |
16130813 |
Appl.
No.: |
07/837,117 |
Filed: |
February 21, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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653232 |
Feb 8, 1991 |
5110388 |
May 5, 1992 |
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380548 |
Jul 14, 1989 |
5118567 |
Jun 2, 1992 |
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Foreign Application Priority Data
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Jul 21, 1988 [JP] |
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63-183158 |
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Current U.S.
Class: |
522/102; 522/103;
522/109; 525/112; 257/E21.505; 257/E21.214 |
Current CPC
Class: |
C09J
4/06 (20130101); H01L 21/6835 (20130101); H01L
21/6836 (20130101); H01L 21/302 (20130101); C09J
7/30 (20180101); C09J 7/22 (20180101); H01L
24/83 (20130101); C09J 7/10 (20180101); C09J
133/08 (20130101); H01L 24/27 (20130101); H01L
24/29 (20130101); C09J 4/06 (20130101); C08F
283/00 (20130101); H01L 2224/29347 (20130101); H01L
2924/01023 (20130101); H01L 2924/01029 (20130101); H01L
2924/01079 (20130101); H01L 2224/2919 (20130101); H01L
2224/2929 (20130101); H01L 2924/07802 (20130101); H01L
2924/01027 (20130101); H01L 2224/29339 (20130101); H01L
2224/29344 (20130101); H01L 2924/01074 (20130101); H01L
2924/0665 (20130101); H01L 2924/01006 (20130101); H01L
2924/01082 (20130101); Y10T 156/1062 (20150115); H01L
2924/01047 (20130101); H01L 2924/14 (20130101); H01L
2224/83191 (20130101); H01L 2924/01019 (20130101); H01L
2924/00013 (20130101); H01L 2224/29324 (20130101); H01L
2924/01005 (20130101); Y10T 428/2809 (20150115); H01L
2924/01013 (20130101); Y10T 428/287 (20150115); H01L
2224/29 (20130101); H01L 2221/68327 (20130101); H01L
2224/29355 (20130101); H01L 2924/01075 (20130101); Y10T
428/2891 (20150115); H01L 2224/29393 (20130101); H01L
2924/01033 (20130101); H01L 2924/01015 (20130101); H01L
2224/274 (20130101); H01L 2224/83855 (20130101); H01L
2221/68336 (20130101); H01L 2224/2919 (20130101); H01L
2924/0665 (20130101); H01L 2224/2919 (20130101); H01L
2924/0635 (20130101); H01L 2224/29344 (20130101); H01L
2924/00014 (20130101); H01L 2224/29339 (20130101); H01L
2924/00014 (20130101); H01L 2224/29347 (20130101); H01L
2924/00014 (20130101); H01L 2224/29355 (20130101); H01L
2924/00014 (20130101); H01L 2224/29324 (20130101); H01L
2924/00014 (20130101); H01L 2224/29393 (20130101); H01L
2924/00014 (20130101); H01L 2224/2929 (20130101); H01L
2924/0665 (20130101); H01L 2924/00012 (20130101); H01L
2924/0665 (20130101); H01L 2924/00 (20130101); H01L
2924/00013 (20130101); H01L 2224/29099 (20130101); H01L
2924/00013 (20130101); H01L 2224/29199 (20130101); H01L
2924/00013 (20130101); H01L 2224/29299 (20130101); H01L
2924/00013 (20130101); H01L 2224/2929 (20130101) |
Current International
Class: |
C09J
7/00 (20060101); C09J 4/06 (20060101); C09J
7/02 (20060101); H01L 21/67 (20060101); H01L
21/02 (20060101); H01L 21/68 (20060101); H01L
21/302 (20060101); H01L 21/58 (20060101); C08F
002/50 (); C09J 004/06 (); C09J 163/02 (); C09J
133/06 () |
Field of
Search: |
;522/109,102,95,103
;525/112 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0157508 |
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Oct 1985 |
|
EP |
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0307919 |
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Mar 1989 |
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EP |
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0221477 |
|
Nov 1985 |
|
JP |
|
1028572 |
|
Feb 1986 |
|
JP |
|
3027580 |
|
Feb 1988 |
|
JP |
|
Primary Examiner: Berman; Susan W.
Attorney, Agent or Firm: Wenderoth, Lind & Ponack
Parent Case Text
This application is a division of Ser. No. 07/653,232 filed Feb. 8,
1991, now U.S. Pat. No. 5,110,388, which is a division of Ser. No.
07/380,548 filed Jul. 14, 1989, now U.S. Pat. No. 5,118,567.
Claims
What is claimed is:
1. An adhesive composition for forming an adhesive layer which is
curable by irradiation with an energy beam and wherein the so cured
adhesive layer is capable of developing tackiness again by heating,
said composition consisting essentially of:
(a) 100 parts by weight of a (meth)acrylate polymer substantially
free from C--C double bonds and having at least 50 mol % of units
derived from at least one (meth)acrylate and a weight average
molecular weight of from about 40,000 to 1,500,000;
(b) from 400 to 2,000 parts by weight of an epoxy resin having an
average of at least 1.8 vicinal epoxy groups per molecule and a
weight average molecular weight of from 100 to 10,000;
(c) from 10 to 1,000 parts by weight of a photopolymerizable low
molecular weight compound having at least one C--C double bond and
having a weight average molecular weight of from 100 to 30,000;
(d) a heat activatable latent curing agent for said epoxy resin;
and
(e) a photopolymerization initiator for said photopolymerizable low
molecular weight compound.
Description
FIELD OF THE INVENTION
The present invention relates to a novel adhesive tape and use
thereof. More particularly, it relates to an adhesive tape suitable
for use in dicing a semiconductor wafer into chips and die-bonding
the chips on a lead frame, and to use of such an adhesive tape.
BACKGROUND OF THE INVENTION
Wafers of semiconductor material such as silicon and
gallium-arsenic having formed thereon integrated circuits have a
relatively large diameter. In the production of integrated circuits
(IC), such a wafer is adhered to an adhesive tape sometimes called
a dicing tape, diced into chips (IC chips), which are then released
(picked up) from the dicing tape, and adhered to (mounted on) a
lead frame by means of an adhesive such as an epoxy resin.
For dicing tapes suitable for use in such a wafer processing
technique, is required that they should exhibit a strong adhesion
to the semiconductor wafer in the step of dicing the wafer into IC
chips on the one hand, while they should also have such a reduced
adhesion to the IC chips in the step of picking up the IC chips so
that the IC chips may be readily released without carrying adhesive
residues from the dicing tapes. Thus, in prior art dicing tapes
adhesive and releasing properties, which are conflicting, are
required, and use of a dicing tape whose adhesive and releasing
properties are not well balanced in wafer processing, invites such
a problem that the dicing and/or picking up steps of the process
cannot be smoothly carried out. In particular, when a prior art
dicing tape is used in wafer processing, a part of the adhesive of
the dicing tape is transferred to the picked up IC chips and
adversely affects the characteristics of the resulting IC.
Accordingly, it has been necessary to remove the undesirable
residual adhesive from the IC chips before they are mounted on a
lead frame. While complete removal of the residual adhesive is
difficult, the step of removing the adhesive not only makes the
processing complicated, but also invites a problem of environmental
pollution if an organic solvent is used, for the removal of the
residual adhesive.
Furthermore, a separate adhesive such as an epoxy resin has been
used for mounting the IC chips on a lead frame, as described in
Japanese Patent Laid-open Publication No. 60-198,757. The use of a
separate adhesive involves another problem such that unceasing
application of appropriate amounts of the adhesive is technically
very difficult, which results in a case of a very small. IC chip in
the applied adhesive frequently bulging out of the chip, whereas in
a case of a relatively large IC chip, the amount of the applied
adhesive tends to be too small to provide a desired adhesion.
OBJECT OF THE INVENTION
The invention intends to solve the above-discussed problems
associated with the prior art and an object of the invention is to
provide an adhesive tape suitable for use in processing
semiconductor wafers which has both actinic radiation curability
and heat curability, which can be used as a dicing tape in the
dicing step and which can provide an adhesive in the mounting
step.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention there is provided an
adhesive tape comprising an energy beam transmittable base sheet
having a surface tension of not more than 40 dyne/cm and an
adhesive layer formed on one surface of said base sheet, said
adhesive layer comprising a (meth)acrylate polymer, an epoxy resin,
a photopolymerizable low molecular weight compound, a heat
activatable latent curing agent for said epoxy resin and a
photopolymerization initiator for said photopolymerizable low
molecular weight compound.
In accordance with another aspect of the invention there is
provided a method for using the abovementioned adhesive tape, which
method comprises the steps of adhering a semiconductor wafer to
said adhesive tape, dicing said wafer into chips together with the
adhesive layer of said adhesive tape, irradiating the adhesive
layer of said tape with an energy beam, picking up the chips
together with pieces of the diced adhesive layer adhered thereto
from said base sheet, placing the chips on a lead frame so that the
respective pieces of the adhesive layer may come in contact with
said lead frame, and causing the pieces of the diced adhesive layer
to again develop tackiness by heating thereby securely mounting the
chips on said lead frame.
In the method according to the invention, the adhesive tape
according to the invention serves as a dicing tape for holding the
wafer in position during the dicing step. Each piece of the diced
and cured adhesive layer, that is attached to each chip and capable
of being tackified by heating, provides an adhesive for securely
mounting the chip on the lead frame in the die-bonding step.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional view of an adhesive tape
according to the invention;
FIGS. 2 to 7 are illustrations showing states of the adhesive tape
of FIG. I in various steps of a wafer processing technique which it
is used; and
FIG. 8 is a cross-sectional view of a modification of the adhesive
tape of FIG. 1
DETAILED DESCRIPTION OF THE INVENTION
The adhesive tape and use thereof according to the invention will
now be described in detail with reference to the accompanying
drawings.
As schematically shown in FIG. 1, the adhesive tape 1 according to
the invention comprises a base sheet 2 and an adhesive layer 3
formed on one surface of the base sheet 2. Before use of the
adhesive tape it is preferable to tentatively apply a strippable
release sheet (not shown) to the adhesive layer 3 for protection
thereof.
It is desirable that the adhesion strength between the base sheet 2
and adhesive layer 3 is initially high and can be reduced by
irradiation to a level sufficiently lower than that between the
adhesive layer and a semiconductor wafer. For this purpose pose the
base sheet 2 should have a surface tension not more than 40
dyne/cm, preferably not more than 38 dyne/cm. Further, suitable as
the base sheet are materials which are low in electrical
conductivity and excellent in water resistance as well as in heat
resistance. From these viewpoints, synthetic resin films are
particularly preferred. As will be stated later, the adhesive tape
according to the invention, when used, is irradiated with an energy
beam such as an electron beam or ultraviolet ray. When it is to be
irradiated with an ultraviolet ray, it must be light transmittable,
but it is not required to be light transmittable, when it is to be
irradiated with an electron beam. Practically, suitable as the base
sheet 2 are films of such synthetic resins as polyester,
polyethylene, polypropylene, polybutene, polybutadiene, vinyl
chloride ionomer, ethylenemethacrylic acid copolymer, vinyl
chloride-urethane copolymer as well as cross-linked films of such
resins. The films may or may not be treated with a silicone.
The base sheet 2 may be either of a single layer or laminated. The
thickness of the base sheet is normally from 25 to 200 .mu.m.
The adhesive layer 3 of the adhesive tape according to the
invention comprises a (meth)acrylate polymer, an epoxy resin, a
photopolymerizable low molecular weight compound, a heat
activatable latent curing agent for the epoxy resin and a
photopolymerization initiator for the photopolymerizable low
molecular weight compound.
By the term "(meth)acrylate polymer" used herein is meant polymers
primarily (at least 50 mol %) comprising structural units derived
from at least one (meth)acrylate i.e. acrylate or methacrylate.
Examples of the suitable (meth)acrylate include, for example,
glycidyl acrylate and methacrylate as well as alkyl and
hydroxyalkyl (meth)acrylates, in which the alkyl moiety has from 1
to 14 carbon atoms, such as methyl, ethyl and butyl acrylates and
methacrylates, and 2-hydroxyethyl acrylate and methacrylate.
The (meth)acrylate polymer which can be used herein may be a
homopolymer of a (meth)acrylate, or it may be a copolymer of at
least two (meth)acrylates. Alternatively, it may be a copolymer of
at least one (meth)acrylate and at least one comonomer
copolymerizable therewith containing at least 50 mol % of units
derived from said at least one (meth)acrylate. Examples of the
comonomer include, for example, acrylic and methacrylic acid,
acrylonitrile, methacrylonitrile, vinyl acetate, vinylpyrrolidones
and vinyl group-containing siloxanes. Particularly preferred
(meth)acrylate polymers which can be used herein are copolymers of
at least one alkyl (meth)acrylate, in which the alkyl moiety has
from 1 to 8 carbon atoms and at least one glycidyl (meth)acrylate
containing up to 80 mol % particular from 5 to 50 mol % of units
derived from said at least one glycidyl (meth)acrylate and,
copolymers of at least one alkyl (meth)acrylate, in which the alkyl
moiety has from 1 to 8 carbon atoms and at least one (meth)acrylic
acid containing up to 50 mol %, in particular from 5 to 20 % mol on
units derived from said at least one (meth)acrylic acid.
The alkyl (meth)acrylate polymer used herein is substantially free
from a C--C double bond, and normally has a weight average
molecular weight of from about 40,000 to about 1,500,000,
preferably from about 100,000 to 1,000.000.
The epoxy resin which can be used herein is an organic material
having an average of at least 1.8 vicinal epoxy groups per
molecule, and normally has a weight average molecular weight of
from 100 to 10000. Examples of the epoxy resin include, for
example, glycidyl ethers of a phenol such as Bisphenol A, Bisphenol
F, resorcinol, phenol novolac and resorcinol novolac; glycidyl
ethers of a polyhydric alcohol such as butanediol, polyethylene
glycol and polypropylene glycol; glycidyl esters of a
polycarboxylic acid such as terephthalic acid, isophthalic acid and
tetrahydrophthalic acid; N,N-diglycidyl and N-alkyl-N-glycidyl
compounds of an aromatic amine such as aniline isocyanurate; and
alicyclic epoxides derived from an alicyclic olefin by oxidation of
its olefinic double bond or bonds, such as vinylcyclohexene
diepoxide, 3,4-epoxycyclohexylmethyl-3,4-dicyclohexane carboxylate
and 2-(3,4-epoxy)cyclohexyl-5,5-spiro (3,4-epoxy)
cyclohexane-m-dioxane. The epoxide compounds illustrated above may
be used alone or in combination. Of these, diglycidyl ethers of a
bisphenol are particularly preferred. As such preferred epoxy resin
those which are commercially available are "Epikote" 828 having a
molecular weight of 380, "Epikote" 834 having a molecular weight of
470, "Epikote" 1001 having a molecular weight of 900, "Epikote"
1002 having a molecular weight of 1060, "Epikote" 1055 having a
molecular weight of 1350 and "Epikote" 100 having a molecular
weight of 2900.
The epoxy resin is used in the adhesive composition for forming the
adhesive layer 3 in an amount of normally from 5 to 2000 parts by
weight, preferably from 100 to 1000 parts by weight, per 100 parts
by weight of the (meth)acrylate polymer.
The photopolymerizable low molecular weight compound which can be
used herein is a compound having at least one carbon-carbon double
bond which is cross-linkable by irradiation with an energy beam
such as an ultraviolet ray and electron beam, and has a weight
average molecular weight of, normally from 100 to 30,000,
preferably from 300 to 10,000. Examples of preferred
photopolymerizable oligomers are those having functional groups
such as hydroxy and carboxy, and include, for example, urethane
acrylate, epoxy acrylate, polyester acrylate, polyether acrylate,
oligomer of (meth)acrylic acid and oligomer of itaconic acid. Of
these, epoxy acrylate and urethane acrylate are particularly
preferred.
The photopolymerizable low molecular weight compound is used in the
adhesive composition for forming the adhesive layer 3 in an amount
of normally from 10 to 1000 parts by weight, preferably from 50 to
600 parts by weight, per 100 parts by weight of the (meth)acrylate
polymer.
The heat activatable latent curing agent for the epoxy resin is a
compound having or potentially having at least two active hydrogen
atoms which are inactive at ambient temperature but are activated,
when heated, to react with the epoxy resin thereby effecting or
promoting curing of the epoxy resin. As such a heat activatable
latent curing agent for the epoxy resin, use can be made of various
onium salts, in particular aliphatic and aromatic sulfonium salts,
and other high melting active hydrogen-containing compounds, alone
or in combination Among others, aliphatic sulfonium salt are
preferred.
The amount of the heat activatable latent curing agent used in the
adhesive composition for forming the adhesive layer 3 may
practically be within the range from 0.1 to 50 parts by weight,
preferably from 1 to 10 parts by weight, per 100 parts by weight of
the epoxy resin, irrespective of the presence of any epoxy groups
in the (meth)acrylate polymer and/or photopolymerizable low
molecular weight compound.
In addition to the heat activatable latent curing agent for epoxide
functionality, a heat curing agent such as a polyisocyanate
compound may be incorporated in adhesive composition for the
purpose of modifying adhesive properties of the adhesive layer.
When used, the amount of the heat curing agent may be normally from
0.1 to 30 parts by weight, and preferably from 5 to 20 parts by
weight, based on 100 parts by weight of the (meth)acrylate
polymer.
The adhesive composition for forming the adhesive layer 3 further
comprises a photopolymerization initiator for the
photopolymerizable low molecular weight compound. Examples of the
photopolymerization initiator include, for example, benzophenone,
acetophenone, benzoin, benzoin alkyl ether, benzil and benzil
dimethylketal, alone or in combination. Of these, alpha-substituted
acetophenones are preferred.
The photopolymerization initiator is used in the adhesive
composition for forming the adhesive layer in an amount of normally
from 0.1 to 10 parts by weight, preferably from 1 to 5 parts by
weight, per 100 parts by weight of the photopolymerizable low
molecular weight compound.
Besides the above-mentioned components, the adhesive layer 3 may be
further incorporated with a leuco dye, a light scattering inorganic
compound, an expanding agent and an antistatic agent.
Examples of the leuco dye include, for example,
3-[N-(p-tolylamino)-7-anilinofluoran and 4,4',
4"-trisdimethylaminotriphenyimethane. The amount of the leuco dye,
when used, is normally from 0.01 to 10 parts by weight per 100
parts by weight of the (meth)acrylate polymer.
As the light scattering agent, suitable is a fine particulate
inorganic compound such as silica and alumina having a particle
size of from 1 to 100 .mu.m, preferably from 1 to 20 .mu.m. The
amount of the light scattering inorganic compound, when used, is
normally from 0.1 to 10 parts by weight per 100 parts by weight of
the (meth)acrylate polymer.
As the expanding agent, use can be made of higher fatty acids and
derivatives thereof, silicone compounds and polyol compounds. The
amount of the expanding agent, when used, is normally from 0.1 to
10 parts by weight per 100 parts by weight of the (meth)acrylate
polymer.
Suitable as the antistatic agent are carbon black and anionic and
cationic surfactants. The amount of the antistatic agent, when
used, is normally from 0.05 to 10 parts by weight per 100 parts by
weight of the (meth)acrylate polymer.
If desired, electrical conductivity may be imparted to the adhesive
layer 3 by incorporating therein an electrically conductive
substance such as gold, silver, copper, nickel, aluminum, stainless
steel and carbon. Such an electrically conductive substance is
preferably used in an amount of from 10 to 400 parts by weight
based on 100 parts by weight of the (meth)acrylate polymer.
The adhesive tape according to the invention can be prepared by
coating the base sheet 2 on one surface thereof with a suitable
adhesive composition for forming the desired adhesive layer 3 by
means of a gravure coater or a bar coater. If desired, necessary
amounts of necessary components for forming the adhesive layer 3
may be dissolved or dispersed in an appropriate solvent,and the
resulting composition may applied on the base sheet 2.
The thickness of the adhesive layer 3 is normally from 3 to 100
.mu.m, and preferably from 10 to 60 .mu.m.
The method for using the adhesive tape 1 of FIG. 1 in wafer
processing will now be described. Reference numbers refer to the
accompanying drawings.
Where a strippable release sheet is provided, it is first removed,
and the adhesive tape 1 is placed, turning the adhesive layer 3
upward (FIG. 1).
On the face side of the adhesive layer 3 is applied a semiconductor
wafer A to be processed (FIG. 2).
In this state the wafer A is diced together with the adhesive layer
3 of the adhesive tape 1 into chips A.sub.1, A.sub.2, A.sub.3 and
so on by a suitable dicing means such as a dicing saw (FIG. 3) . In
this step, the wafer A is completely diced into chips, whereas the
adhesive layer 3 is substantially diced. In other words, at least
50%, preferably 100% of the whole thickness of the adhesive layer
is cut. The deeper the cut, the better.
The base sheet 2 is then expanded in two perpendicularly
intersecting directions within the plane of the sheet to facilitate
the subsequent picking up operation (FIG. 4). While the illustrated
method involves a step of expanding, this step is not always
necessary. In a case wherein this stem is carried out, the base
sheet 2 should naturally have extensibility in machine and
transverse directions . However, base sheets having no
extensibility may also be used where no expansion treatment is
carried out.
Before the chips are picked up, the adhesive layer 3 is irradiated
with energy beam B to polymerize or cure the photopolymerizable
compound contained in the adhesive layer 3 from the side of the
base sheet 2 on which the adhesive layer 3 is not formed (FIG. 4 )
. As the energy beam ultraviolet ray having a center wave length of
about 365 nm is preferred, and upon irradiation with such
ultraviolet ray intensity of radiation and irradiation time are
preferably set within the ranges of from 20 to 500 mW/cm.sup.2 and
from 0.1 to 150 seconds, respectively.
While the dicing step is carried out prior to the irradiation step
in the illustrated method, the irradiation may be effected prior to
the dicing, in particular where no expansion is carried out.
Furthermore, while the irradiation in the illustrated method is
carried out before the chips come to a pick-up station where the
pick-up operation is carried out, the irradiation may be effected
at the pick-up station, in particular where the expansion carried
out.
When the adhesive used herein is cured by irradiation with an
energy beam, its adhesion strength to the wafer is increased well
above a level of its adhesion strength to the base sheet. This is
believed to be due to the presence of the epoxy resin in the
adhesive.
Next, in a pick-up station, the wafer chips A.sub.1, A.sub.2,
A.sub.3 and so on are successively pushed up by a pushing rod (not
shown), picked up from the base sheet 2 by a suitable means, such
as a vacuum collet 6, as shown in FIG. 5, and collected in a wafer
box (not shown). Since the cured adhesive has a greater adhesion
strength to the wafer than to the base sheet 1, the wafer chips can
readily be released together with the cured adhesive attached
thereto from the base sheet 1. FIG. 6 depicts the wafer chip
A.sub.1 picked up by the vacuum collet 6. As seen from FIG. 6, the
picked up wafer chip A.sub.1 carries a piece 3.sub.1 of the diced
and irradiated adhesive layer 3. Since the cured adhesive attached
to the wafer chips is no longer sticky, the wafer chips collected
in the wafer box do not stick to each other.
In the illustrated method the energy beam irradiation is effected
at once, but it may be done partially in several times. For
instance, especially, in a case wherein the expansion of the base
sheet has been carried out, only the portion of the base sheet 1
corresponding to each of the wafer chips A.sub.1, A.sub.2, A.sub.3
and so on may be irradiated from the back side of the base sheet 1
by means of an irradiating tube, pushed up by the same tube and
picked up by the vacuum collect so that the irradiation may be
carried out at the pick-up station.
The wafer chips A.sub.1, A.sub.2, A.sub.3 and so on are then placed
on a lead frame 7 by means of a die-bonder (not shown) so that the
respective pieces 3.sub.1, 3.sub.2, 3.sub.3 and so on of the
adhesive layer may come in contact with the lead frame, and heated
at a temperature of normally from 100.degree. to 300.degree. C.,
preferably from 150.degree. to 250.degree. C., for a period of
normally from 1 to 120 minutes, preferably from 5 to 60 minutes so
as to cause the cured adhesive contained in the pieces of the diced
adhesive layer to again develop tackiness (FIG. 7). By this heating
the adhesion strength of the adhesive layer to the wafer chip is
increased to at least 1000 g/25 mm, and at the same time the wafer
chips are firmly adhered to the lead frame 7 at an adhesion
strength of substantially the same level. Thus, the wafer chips can
be securely mounted the on lead frame 7.
In accordance with still another aspect of the invention there is
provided an adhesive composition comprising a (meth)acrylate
polymer having at least 50 mol % of units derived from at least one
(meth)acrylate, from 5 to 2000 parts by weight, based on 100 parts
by weight of the (meth)acrylate polymer, of an epoxy resin having a
weight average molecular weight of from 100 to 10000, from 10 to
1000 parts by weight, based on 100 parts by weight of the
(meth)acrylate polymer, of a photopolymerizable low molecular
weight compound having a weight average molecular weight of from
100 to 30,000, a heat activatable latent curing agent for said
epoxy resin and a photopolymerization initiator for said
photopolymerizable low molecular weight compound.
The adhesive composition according to the invention provides an
adhesive layer which is curable by irradiation with an energy beam
and the so cured adhesive layer is capable of developing tackiness
again by heating.
The invention will now be further described by the following
examples, wherein parts are by weight unless otherwise
specified.
EXAMPLE 1
______________________________________ (Meth)acrylate polymer
having a solid 100 parts content of 35% by weight and (solid basis)
containing a copolymer of methyl acrylate and glycidyl
methacrylate, the copolymer containing 20 mol % methyl acrylate and
having a molecular weight of about 300,000 Bisphenol diglycidyl
ether based 600 parts epoxy resin having a number average molecular
weight of 500 (supplied by YUKA SHELL EPOXY K. K. under a trade
name of Epikote 834) Photopolymerizable epoxy acrylate 100 parts
oligomer having two C--C double bonds and a molecular weight of 730
as measured by GPC using polystyrene as standard (supplied by SHIN-
NAKAMURA CHEMICAL Co, Ltd. under a trade name of NK-ester EA-800)
Heat activatable latent curing 18 parts agent for epoxy resins:
aliphatic sulfonium salt (supplied by ASAHI DENKA KOGYO K. K. under
a trade name of CP-66) Photopolymerization initiator: 5 parts
2.2-dimethoxy-2-phenylacetophenone
______________________________________
An adhesive composition comprising the above-indicated components
in indicated amounts was applied on a polyethylene film having a
surface tension of 32 dyne/cm and a thickness of 100 .mu.m, and
dried under heating at 100.degree. C. for 1 minute to prepare an
adhesive tape having an adhesive layer of a thickness of 30
.mu.m.
A silicon wafer was applied onto the adhesive layer surface of the
adhesive tape so prepared. The adhesive tape adhered to the silicon
wafer at an adhesion strength of 360 g/25 mm, as measured in
accordance with JIS Z 0237. The adhesive layer was then irradiated
with 200 mW/cm.sup.2 of an ultraviolet ray for 2 seconds using a 80
W/cm high pressure mercury lamp. By this irradiation the adhesion
strength between the adhesive layer and the silicon wafer increased
to 900 g/25 mm, while the adhesion strength between the adhesive
layer and the polyethylene base sheet after the irradiation was 60
g/25 mm.
The adhesive tape was employed in processing a silicon wafer as
follows. A silicon wafer of the same quality having a diameter of 5
inches was applied onto the adhesive layer of the tape, and fully
cut together with the adhesive layer by means of a dicing saw
supplied by DISCO Co., Lid.at a cutting rate of 50 mm/sec into 5 mm
square IC chips. The adhesive layer was irradiated through the
polyethylene base sheet with the above-mentioned ultraviolet ray
for 2 seconds. The IC chips were picked up and then directly placed
on a lead frame by means of a die-bonder so that pieces of the
cured adhesive layer attached to the chips may come in contact with
the lead frame. The chips were then heated at a temperature of
170.degree. C. for a period of 30 minutes whereby they could be
securely mounted on the lead frame.
EXAMPLE 2
______________________________________ (Meth)acrylate polymer
having a solid 100 parts content of 35% by weight and containing
(solid basis) a copolymer of butyl acrylate and acrylic acid, the
copolymer containing 80 mol % of butyl acrylate and having a
molecular weight of about 500,000 Bisphenol diglycidyl ether based
400 parts epoxy resin having a solid content of (solid basis) 30%
by weight and a number average molecular weight of 900 (supplied by
YUKA SHELL EPOXY K. K. under a trade name of Epikote 1001)
Photopolymerizable urethane acrylate 70 parts oligomer having two
C--C double bonds and a molecular weight of 5,000 as measured by
GPC using polystyrene as standard (supplied by DAINICHISEIKA COLOR
& MFG. CO., LTD. under a trade name of 14-33) Heat activatable
latent curing 8 parts agent for epoxy resins: aliphatic sulfonium
salt (supplied by ASAHI DENKA KOGYO K. K. under a trade name of
CP-66) Photopolymerization initiator: 5 parts
2.2-dimethoxy-2-phenylacetophenone Heat curing agent: aromatic 5
parts polyisocyanate (supplied by TOYO INK MFG. CO. LTD. under a
trade name of BHS-8515) Electrically conductive filler: 750 parts
particulate nickel having a particle size of 5 .mu.m
______________________________________
An adhesive composition comprising the above-indicated components
in indicated amounts was applied on a polypropylene film having a
surface tension of 35 dyne/cm and a thickness of 60 .mu.m, and
dried under heating at 100.degree. C. for 1 minute to prepare an
adhesive tape having an adhesive layer of a thickness of 30
.mu.m.
A silicon wafer was applied onto the adhesive layer surface of the
adhesive tape so prepared. The adhesive tape adhered to the silicon
wafer at an adhesion strength of 150 g/25 .mu.mm. The adhesive
layer was then irradiated with an ultraviolet ray as in Example 1.
By this irradiation the adhesion strength between the-adhesive
layer and the silicon wafer increased to 500 g/25 mm, while the
adhesion strength between the adhesive layer and the polypropylene
base sheet after the irradiation was to 40 g/25 mm.
The adhesive tape was employed in processing a silicon wafer in the
manner as described in Example 1. Good results were obtained as in
Example 1.
Effect of the Invention
The adhesive layer of the adhesive tape according to the invention
can be cured by irradiation with an energy beam, and the so cured
adhesive layer is capable of developing tackiness again by heating.
Furthermore, the adhesive tape has such a unique property that when
it is adhered to a semiconductor wafer and irradiated with an
energy beam, the adhesion strength of the adhesive layer to the
wafer becomes much higher than that to the base sheet. These
properties of the adhesive tape according to the invention can be
advantageously utilized in processing a semiconductor wafer
according to the invention.
In the method according to the invention, the adhesive tape
according to the invention serves as a dicing tape for holding the
wafer in position during the dicing step. Each piece of the diced
and cured adhesive layer, that is attached to each chip and capable
of being tackified by heating, provides an adhesive required for
securely mounting the chip on the lead frame in the die-bonding
step. Thus, the invention has solved the problems associated with
the prior art including removal of any residual adhesive from diced
IC chips and adequate provision of a separate adhesive to the IC
chips.
Modification of the Invention
According to one modification of the invention there is provided an
adhesive tape comprising an adhesive layer composed of a
(meth)acrylate polymer, an epoxy resin, a photopolymerizable low
molecular weight compound, a heat activatable latent curing agent
for said epoxy resin and a photopolymerization initiator for said
photopolymerizable low molecular weight compound.
Such a base sheet free adhesive tape can be readily prepared by
forming the adhesive layer 3 on a release base 8 (FIG. 8), and can
also be used in processing a semiconductor wafer. Normally, a base
sheet free adhesive tape is supplied to customers in a form
sandwiched between a pair of release sheets. Upon use thereof in
wafer processing, one of the release sheets is removed to expose
the adhesive layer 3; a semiconductor wafer to be processed is
adhered to the adhesive layer; the adhesive layer is irradiated
with an energy beam transmitted through the remaining release
sheet; the wafer is diced into chips together with the adhesive
layer; the chips are picked up together with pieces of the
irradiated and diced adhesive layer from the release sheet and
placed on a lead frame so that the respective pieces of the
adhesive layer adhered thereto may come in contact with said lead
frame; and the pieces of the diced adhesive layer are caused to
again develop tackiness by heating, thereby securely mounting the
chips on said lead frame.
Thus, according to another modification of the invention there is
provided a method for using an adhesive tape comprising an adhesive
layer composed of a (meth)acrylate polymer, an epoxy resin, a
photopolymerizable low molecular weight compound, a heat
activatable latent curing agent for said epoxy resin and a
photopolymerization initiator for said photopolymerizable low
molecular weight compound, said method comprising the steps of
adhering a semiconductor wafer to said adhesive tape formed on a
release sheet, irradiating the adhesive layer with an energy beam
dicing said wafer into chips together with the adhesive layer,
picking up the chips together with pieces of the diced adhesive
layer adhered thereto from said release sheet, placing the chips
together with pieces of the diced adhesive layer adhered thereto on
a lead frame so that the respective pieces of the adhesive layer
may come in contact with said lead frame, and causing the pieces of
the diced adhesive layer to again develop tackiness by heating,
thereby securely mounting the chips on said lead frame.
* * * * *